1. Field of the Invention
The present invention relates to a process for the production of 1,1,1-trifluoro-2,2-dichloroethane. Particularly, the present invention relates to a process for the production of 1,1,1-trifluoro-2,2-dichloroethane comprising chlorination of 1,1,1-trifluoro-2-chloroethane with chlorine gas in the presence or absence of a metal salt as a catalyst.
2. Description of the Related Art
1,1,1-Trifluoro-2,2-dichloroethane is expected to replace trichlorofluoromethane, since it does not decompose ozone in the stratosphere. Thus, it is desirable to develop an economical process for the production of 1,1,1-trifluoro-2,2-dichloroethane.
Several processes for the production of 1,1,1-trifluoro-2,2-dichloroethane have been already proposed. For example, Czechoslovakian Patent No. 136,735 and Japanese Patent Kokai Publication No. 222038/1983 describe a process comprising reduction of 1,1,1-trifluoro-2,2,2-trichloroethane. Japanese Patent Publication No. 27375/1986 describes a process comprising isomerization of 1,1,2-trifluoro-1,2-dichloroethane. U.S. Pat. No. 3,755,477 describes a process comprising fluorination of ethylene tetrachloride. Japanese Patent Kokai Publication No. 82711/1978 describes a process comprising photo chlorination of 1,1,1-trifluoro-2-chloroethane. McBee describes a process comprising chlorination of 1,1,1-trifluoroethane in J. Ind. Eng. Chem., 39, 409, (1947).
However, from a point of view of the economical production, the above known processes for the production of 1,1,1.trifluoro-2,2-dichloroethane are not necessarily suitable since the yield and selectivity through such processes are not sufficiently high.
McBee describes that 1,1,1-trifluoroethane, which is a compound which is similar to a starting material for the production of 1,1,1-trifluoro-2,2-dichloroethane, reacts at a reaction temperature of 485.degree. C. with chlorine at a molar ratio of 1:1. Under these conditions, the conversion of 1,1,1-trifluoroethane is 50%. The product produced by this process contains 22.5% of 1,1,1-trifluoro-2,2-dichloroethane and 41.8% of 1,1,1-trifluoro-2,2,2-trichloroethane. It has been reported that, judging from the fact that the amounts of the compounds of which all hydrogen atoms are replaced with chlorine atoms have been increased, the chlorination rate increases, as the chlorination proceeds, or as the number of hydrogen atoms replaced with chlorine atoms increases.
Accordingly, the above report indicates that the molar ratio of 1,1,1-trifluoro-2,2,2-trichloroethane to 1,1,1-trifluoro-2,2-dichloroethane is more than 1, that is, the amount of 1,1,1-trifluoro-2,2,2-trichloroethane produced is always more than 1,1,1-trifluoro-2,2-dichloroethane.